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<head>
    <meta charset="UTF-8">
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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>set 实践</title>
</head>

<body>
    <script>
        let arr = [1, 2, 3, 4, 5, 4, 3, 2, 1];
        //1.数组去重
        // let result = [...new Set(arr)];
        // console.log(result);
        //2.交集
        let arr2 = [4, 5, 6, 5];
        let res = [...new Set(arr)].filter(item => {
            let s2 = new Set(arr2);//4,5,6
            if (s2.has(item)) {
                return true;
            } else {
                return false;
            }
        });
        console.log('res',res);

        // let res2 = [...new Set(arr)].filter(item => new Set(arr2).has(item));
        // console.log(res2);

        //3.并集
        // let unio = [...new Set([...arr, ...arr2])];
        // console.log(unio);

        //4.差集
        let diff = [...new Set(arr)].filter(item => !(new Set(arr2).has(item)));
        console.log(diff);



    </script>


</body>

</html>